Affected Products=================Confirmed in Microsoft Lync Server 2010, version 4.0.7577.0. Other versions may also be affected.

Details========Microsoft Lync 2010, version 4.0.7577.4087, fails to sanitize the “User-Agent Header” for meet.domainame.com.

By inserting JavaScript into the aforementioned parameters and stacking commands, an attacker can execute arbitrary commands in the context of the application.

Impact=======Malicious users could execute arbitrary applications on the client systems, compromising the confidentiality, integrity and availability of information on the client system.

Solution========The vendor should implement thorough input validation in order to remove dangerous characters from user supplied data. Additionally, the vendor should implement thorough output encoding in order to display, and not execute, dangerous characters within the browser.

Proof-of-Concept (PoC)===================The following Request is included as a proof of concept. The proof of concept is designed to open notepad.exe when the Request is received by the server.

Vendor Statement (from Microsoft Security Response Center)================The vulnerability described in this report is a XSS vulnerability in the User-Agent which requires an attacker to be in a man-in-the middle situation in order to be able to modify the User-Agent. In a default configuration of Lync server, TLS encryption is used to protect against this type of attack. Customers concerned about this issue should check their environments to ensure that Lync is configured to use TLS to encrypt all traffic, a default configuration.